I don't know if we can answer this for sure at the moment given the ongoing
discussion on shared, but looking at core.sync, it occurred to me that there's
a major problem with the classes in there. None of the work with shared. And
unless I'm missing something here, I don't see how many of them are even
useful as anything other than shared. After all, what good is a mutex which is
thread-local? But none of the methods on Mutex or its friends are shared.
So, the question is should the all have their methods shared? And if they
should, is there any reason to have non-shared overloads for them? What good
are they as anything other than shared? How is anyone using them right now?
- Jonathan M Davis

I don't know if we can answer this for sure at the moment given the ongoing
discussion on shared, but looking at core.sync, it occurred to me that there's
a major problem with the classes in there. None of the work with shared. And
unless I'm missing something here, I don't see how many of them are even
useful as anything other than shared. After all, what good is a mutex which is
thread-local? But none of the methods on Mutex or its friends are shared.
So, the question is should the all have their methods shared? And if they
should, is there any reason to have non-shared overloads for them? What good
are they as anything other than shared? How is anyone using them right now?
- Jonathan M Davis

Not at this point in time. It would break a ridiculous amount of code if
we did this, given the current extremely annoying nature of shared.
Most D code I have seen in the wild just shares mutexes, conditions, etc
with __gshared or some other mechanism anyway, so I don't think there's
anything to gain. Like, what would shared actually buy you here?
--
Alex Rønne Petersen
alex lycus.org
http://lycus.org

ongoing
discussion on shared, but looking at core.sync, it occurred to me t=

hat

there's a major problem with the classes in there. None of the work=

with

shared. And unless I'm missing something here, I don't see how many=

of

them are even useful as anything other than shared. After all, what=

good

is a mutex which is thread-local? But none of the methods on Mutex =

or its

friends are shared.
=20
So, the question is should the all have their methods shared? And i=

f they

should, is there any reason to have non-shared overloads for them? =

What

good are they as anything other than shared? How is anyone using th=

em

right now?
=20
- Jonathan M Davis

=20
Not at this point in time. It would break a ridiculous amount of code=

if

we did this, given the current extremely annoying nature of shared.
=20
Most D code I have seen in the wild just shares mutexes, conditions, =

etc

with __gshared or some other mechanism anyway, so I don't think there=

's

anything to gain. Like, what would shared actually buy you here?

__gshared is a good reason for leaving non-shared overloads, but isn't =
code=20
really supposed to be using shared and not __gshared unless it's specif=
ically=20
extern(C)? That being the case, I'd expect shared to be the correct thi=
ng to=20
use with mutexes normally, and right now, that won't work without a ton=
of=20
casting or adding shared overloads.
- Jonathan M Davis

I don't know if we can answer this for sure at the moment given the
ongoing
discussion on shared, but looking at core.sync, it occurred to me that
there's a major problem with the classes in there. None of the work with
shared. And unless I'm missing something here, I don't see how many of
them are even useful as anything other than shared. After all, what good
is a mutex which is thread-local? But none of the methods on Mutex or its
friends are shared.
So, the question is should the all have their methods shared? And if they
should, is there any reason to have non-shared overloads for them? What
good are they as anything other than shared? How is anyone using them
right now?
- Jonathan M Davis

Not at this point in time. It would break a ridiculous amount of code if
we did this, given the current extremely annoying nature of shared.
Most D code I have seen in the wild just shares mutexes, conditions, etc
with __gshared or some other mechanism anyway, so I don't think there's
anything to gain. Like, what would shared actually buy you here?

__gshared is a good reason for leaving non-shared overloads, but isn't code
really supposed to be using shared and not __gshared unless it's specifically
extern(C)? That being the case, I'd expect shared to be the correct thing to
use with mutexes normally, and right now, that won't work without a ton of
casting or adding shared overloads.
- Jonathan M Davis

I don't know what anything that has to do with shared is supposed or not
supposed to do. It is not clear, even to the primary language designers,
what shared actually is, so I really can't say anything to this...
All I can say is, let's wait with this until we know what shared is
going to actually do. We don't want to do something we'll regret later.
--
Alex Rønne Petersen
alex lycus.org
http://lycus.org

I don't know if we can answer this for sure at the moment given the
ongoing
discussion on shared, but looking at core.sync, it occurred to me that
there's a major problem with the classes in there. None of the work
with
shared. And unless I'm missing something here, I don't see how many of
them are even useful as anything other than shared. After all, what
good
is a mutex which is thread-local? But none of the methods on Mutex
or its
friends are shared.
So, the question is should the all have their methods shared? And if
they
should, is there any reason to have non-shared overloads for them? What
good are they as anything other than shared? How is anyone using them
right now?
- Jonathan M Davis

Not at this point in time. It would break a ridiculous amount of code if
we did this, given the current extremely annoying nature of shared.
Most D code I have seen in the wild just shares mutexes, conditions, etc
with __gshared or some other mechanism anyway, so I don't think there's
anything to gain. Like, what would shared actually buy you here?

__gshared is a good reason for leaving non-shared overloads, but isn't
code
really supposed to be using shared and not __gshared unless it's
specifically
extern(C)? That being the case, I'd expect shared to be the correct
thing to
use with mutexes normally, and right now, that won't work without a
ton of
casting or adding shared overloads.
- Jonathan M Davis

I don't know what anything that has to do with shared is supposed or not
supposed to do. It is not clear, even to the primary language designers,
what shared actually is, so I really can't say anything to this...

Let's please stop this mantra. It buy us nothing but FUD.
One thing is clear - shared is not going away over night. Yes, having
auto-magic atomic ops for various builtins is discussed, the kind of
memory model is discussed.
Everything else stays. It's the globally shared data and it has tight
restrictions on what you can do with it. As such it is (just like
immutable) is safely passable between threads.

All I can say is, let's wait with this until we know what shared is
going to actually do. We don't want to do something we'll regret later.

Obviously we know what shared is. It's just certain details need
straightening up. And certainly druntime/std.concurrency should add more
support for it where meaningful.
--
Dmitry Olshansky

I don't know if we can answer this for sure at the moment given the
ongoing
discussion on shared, but looking at core.sync, it occurred to me that
there's a major problem with the classes in there. None of the work
with
shared. And unless I'm missing something here, I don't see how many of
them are even useful as anything other than shared. After all, what
good
is a mutex which is thread-local? But none of the methods on Mutex
or its
friends are shared.
So, the question is should the all have their methods shared? And if
they
should, is there any reason to have non-shared overloads for them?
What
good are they as anything other than shared? How is anyone using them
right now?
- Jonathan M Davis

Not at this point in time. It would break a ridiculous amount of
code if
we did this, given the current extremely annoying nature of shared.
Most D code I have seen in the wild just shares mutexes, conditions,
etc
with __gshared or some other mechanism anyway, so I don't think there's
anything to gain. Like, what would shared actually buy you here?

__gshared is a good reason for leaving non-shared overloads, but isn't
code
really supposed to be using shared and not __gshared unless it's
specifically
extern(C)? That being the case, I'd expect shared to be the correct
thing to
use with mutexes normally, and right now, that won't work without a
ton of
casting or adding shared overloads.
- Jonathan M Davis

I don't know what anything that has to do with shared is supposed or not
supposed to do. It is not clear, even to the primary language designers,
what shared actually is, so I really can't say anything to this...

Let's please stop this mantra. It buy us nothing but FUD.
One thing is clear - shared is not going away over night. Yes, having
auto-magic atomic ops for various builtins is discussed, the kind of
memory model is discussed.
Everything else stays. It's the globally shared data and it has tight
restrictions on what you can do with it. As such it is (just like
immutable) is safely passable between threads.

There have been proposals to a completely different meaning of shared
that has nothing to do with memory models or atomic ops. There is no FUD
here. Shoehorning shared in its current state into core.sync is just
plain unreasonable given that nothing has been set in stone about the
meaning of shared at all yet.

All I can say is, let's wait with this until we know what shared is
going to actually do. We don't want to do something we'll regret later.

Obviously we know what shared is. It's just certain details need
straightening up. And certainly druntime/std.concurrency should add more
support for it where meaningful.

We don't know at all what shared is. Have you been following the other
thread? People have wildly different ideas of what it should do.
I don't see why we should be in a hurry to add shared to core.sync in
particular. Practically all of the runtime and standard library can't
work properly with shared anyway, so it's not going to change a whole
lot. I think it's much more sensible to wait until shared's semantics
are set in stone and *then* start adapting the runtime and standard library.
I can't stop anyone from just doing this, of course, but it seems like a
premature change to me.
--
Alex Rønne Petersen
alex lycus.org
http://lycus.org

Everything else stays. It's the globally shared data and it has tight
restrictions on what you can do with it. As such it is (just like
immutable) is safely passable between threads.

There have been proposals to a completely different meaning of shared
that has nothing to do with memory models or atomic ops. There is no FUD
here. Shoehorning shared in its current state into core.sync is just
plain unreasonable given that nothing has been set in stone about the
meaning of shared at all yet.

I'd argue that shared on these objects has nothing to do with memory
models and atomics. It's about global visibility and access to API that
is interlocked on OS-level anyway. It works with any sane definition
that doesn't forget to add that 'shared' implies global visibility.

All I can say is, let's wait with this until we know what shared is
going to actually do. We don't want to do something we'll regret later.

Obviously we know what shared is. It's just certain details need
straightening up. And certainly druntime/std.concurrency should add more
support for it where meaningful.

We don't know at all what shared is. Have you been following the other
thread? People have wildly different ideas of what it should do.

I admit dismissing a lot of proposals from that thread on sight. The
ones being about shared somehow 'just working' and getting you safe way
to sharing and the one about auto-magically attaching mutexes to shared
stuff.
Given now that the thread is mostly spent. If there many good different
concepts I'd appreciate if you list these here.

I don't see why we should be in a hurry to add shared to core.sync in
particular.

Practically all of the runtime and standard library can't
work properly with shared anyway, so it's not going to change a whole
lot.

In part because even things that are supposed to always be shared in
fact are not working as shared. And that's because nobody have found the
time to go on and do this work.
Add the fact that say class instances have monitor field when everything
is TLS by default for me is indication of one thing only - during a move
to TLS by default and shared a lot of things were not updated
accordingly because of the lack of time and other issues.

I think it's much more sensible to wait until shared's semantics
are set in stone and *then* start adapting the runtime and standard
library.
I can't stop anyone from just doing this, of course, but it seems like a
premature change to me.

What change in semantics of shared could stop mutex object from making
sense only as a shared object? I mean the kind of change that can
realistically can happen not some vague idea.
--
Dmitry Olshansky

What change in semantics of shared could stop mutex object from making
sense only as a shared object? I mean the kind of change that can
realistically can happen not some vague idea.

I thought that it was blindingly clear from TDPL and even the online spec what
shared is for. It marks variables as being shared across threads rather than
thread local. I don't see how that could possibly be changing. __gshared isn't
even _mentioned_ in TDPL, and I think that it gets used as much as it does is
entirely because of some of the current issues with shared's implementation in
the compiler and the lack of support in druntime and Phobos.
There are definitely questions as to what exactly should happen when a variable
is marked as shared, but they have to do with what protections you get and
what conversions are possible. They still don't fundamentally change the fact
that the point of shared is to share an instance across threads rather than
have it be thread local like everything is by default.
So, I concur in that I don't see how the semantics of shared could possibly
not be appropriate for mutexes. I started this thread primarily because I was
shocked that Mutex, Condition, etc. weren't marked with shared already, and I
didn't see how they could even be used without it (and apparently, the answer
to that is that almost everyone cops out and uses __gshared).
- Jonathan M Davis

To separate an important notion I'm trying to express.
I assume that:
class X{
...
shared foo(...);
void bar(...);
...
}
shared X sharedStuff;
X localStuff;
Implies under any viable definition of shared that (including the
current one and any pending clarifications):
a) foo can be called with sharedStuff in multiple threads at the same
time. Thus it has to be thread safe (irregardless of possible
system/ trusted hackery inside).
b) localStuff on the other hand can called with bar (and any non-shared
methods) only in a single thread at any time. If localStuff is defined
at global scope each thread has its own copy thus this requirement is
fulfilled kind of automatically.
The major benefits of shared lie in cleaning up the opposite - unshared
stuff. Having shared enables us to archieve great things we haven't
looked at yet (maybe because of bugs/issues in the other departments).
I'll name a few.
We can have lock-less and _safe_ file I/O by default unlike e.g. C and
pretty much everybody else. I should have said safe & _faster_ by
default. This is why I believe D should stop relying on C's I/O as
anything but fallback. We even had a partially complete design for new
std.io that does it.
Same goes for memory allocations - lock-less thread-local allocators are
possible _safely_ and by default (though it would have to go to the OS
from time to time and likely to lock something here). It's not explored
and remains as unused potential.
--
Dmitry Olshansky

=20
So, I concur in that I don't see how the semantics of shared could =

possibly=20

not be appropriate for mutexes. I started this thread primarily =

because I was=20

shocked that Mutex, Condition, etc. weren't marked with shared =

already, and I=20

didn't see how they could even be used without it (and apparently, the =

answer=20

to that is that almost everyone cops out and uses __gshared).

I tried this once and it cascaded to requiring modifications of various =
definitions on core.sys.posix to add a "shared" qualifier, and since I =
wasn't ready to do that I rolled back the changes. I guess the =
alternative would be to have a shared equivalent for every operation =
that basically just casts away shared and then calls the non-shared =
function, but that's such a terrible design I've been resisting it.=

I don't know if we can answer this for sure at the moment given the ongoing
discussion on shared, but looking at core.sync, it occurred to me that there's
a major problem with the classes in there. None of the work with shared. And
unless I'm missing something here, I don't see how many of them are even
useful as anything other than shared. After all, what good is a mutex which is
thread-local? But none of the methods on Mutex or its friends are shared.

None of them are useful without shared.They should work with shared, but
that'll break code outright. I think 2 overloads per method with TLS
versions going through the deprecation path.

So, the question is should the all have their methods shared? And if they
should, is there any reason to have non-shared overloads for them? What good
are they as anything other than shared? How is anyone using them right now?

I do suspect that most people use _gshared with them as it is the less
painful way. Another way is to have them shared and cast them to TLS as
needed. Since mutex, condition etc. are opaque types around OS
primitives TLS doesn't make sense at all but currently allows to call
their methods.
--
Dmitry Olshansky

So, I concur in that I don't see how the semantics of shared could
possibly
not be appropriate for mutexes. I started this thread primarily because I
was shocked that Mutex, Condition, etc. weren't marked with shared
already, and I didn't see how they could even be used without it (and
apparently, the answer to that is that almost everyone cops out and uses
__gshared).

I tried this once and it cascaded to requiring modifications of various
definitions on core.sys.posix to add a "shared" qualifier, and since I
wasn't ready to do that I rolled back the changes. I guess the alternative
would be to have a shared equivalent for every operation that basically
just casts away shared and then calls the non-shared function, but that's
such a terrible design I've been resisting it.

Well, this is certainly going to need to be sorted out. And given that it's
not unreasonable that both shared and __gshared be used with the type is
core.sync, I don't think we have much choice to duplicate most of those
functions (probably using casting internally to avoid actually duplicating the
implementation in most cases) unless __gshared becomes implicitly convertible
to shared.
- Jonathan M Davis